The present invention relates to a drive and read/write apparatus for an optical disk, more particularly to a drive and read/write apparatus for a rewritable optical disk.
The present invention also relates to an improved bias magnet device for magneto-optical disk drive and read/write apparatus.
The present invention also relates to an improved device for positioning the optical head of an optical disk drive and read/write apparatus, particularly to shorten the access time thereof.
The present invention furthermore relates to an optical disk drive and read/write apparatus, and more particularly relates to an improved drive and read/write apparatus appropriate to record or write information in an optical disk on both the sides thereof.
The present invention still further relates to a divided-type optical head for an optical disk drive and read/write apparatus, and more particularly relates to a divided-type optical head improved to effectively prevent the efficiency of concentration of a laser beam from being deteriorated by the fluctuation in the posture of the movable optical system of the head.
FIG. 23 shows a conventional drive and read/write apparatus for an optical disk. The apparatus is a magneto-optical disk drive and read/write apparatus including only one optical head 5 in such a position as to be opposed to a bias magnet 13 across the magneto-optical disk 4. In the apparatus, a motor 3 for rotating a turntable 2 at a prescribed speed is provided on the base of a housing 1 so that the disk 4 clamped to the turntable by a loading mechanism not shown in the drawing can be turned at an accurate speed by the motor. The optical head 5 is moved by a linear motor 6 so as to be opposed to a prescribed position on the disk 4 to read or write data from or in the disk, namely, to reproduce or erase and record signals.
When new data is to be written or recorded in the optical disk 4 by the apparatus, a laser beam 8 is horizontally emitted from a semiconductor laser module 7, transmitted through a polarized beam splitter 9, diverted upward by a prism 10, and concentrated to the written or recorded position of the data in the disk through an objective lens 11 to heat the beam-irradiated portion of the disk above the Curie temperature thereof by the spot of the beam thereon to magnetize the portion in the direction of the magnetic field of the bias magnet 13 to erase existing data from the portion first. By the time the disk 4 is then rotated by another round to have the same positional relationship with the head 5 and the magnet 13 as at the time of erasure, a direction is selected for the magnetic field of the magnet so as to be coincident with the direction of magnetization of the portion for the writing or recording of the new data. The portion is then heated by the spot of the beam thereon so that the new data is written or recorded in the portion through the magnetization thereof in the selected direction. The disk 4 is turned by yet another round to check whether the new data have been precisely written or recorded in the portion of the disk, if necessary.
When data is to be read or reproduced from the disk 4 by the apparatus, the intensity of the laser beam 8 is made lower than at the time of the writing or recording of data in the disk so as to heat the beam-irradiated portion thereof below the Curie temperature of the disk. The optical head 5 is moved to be opposed to the portion from which the data is to be read or reproduced. The laser beam 8 is then irradiated upon the portion. The direction of rotation of the plane of polarization of light 14 reflected by the portion changes depending on the direction of the magnetization of the magneto-optical film of the portion. The changed direction is detected to read or reproduce the data from the portion.
In the apparatus, a shaft 2a supporting the turntable 2 is rotatably supported with two ball bearings 2b. The optical head 5 is coupled to the linear motor 6 so that the head can be straightly moved along the radial direction of the disk 4 by the motor in order to be opposed to the aimed track of the disk.
The disk 4 is used as it remains housed in a conventional cassette 15 shown in FIGS. 24 and 25. The cassette 15 includes a body 17 in which the disk 4 is housed, and a shutter 19 for opening and closing the openings 18a and 18b of the upper and lower sides of the body. If the disk 4 has a data storage portion on only one side of the disk, the lower side of the body 17 of the cassette 15 has the opening 18 as a passage corresponding to the range of the movement of the optical head 5, and the other opening 18b as a center hole corresponding to the hub 16 of the disk 4 to clamp it to the turntable 2, and the upper side of the body has the yet other opening 18a as a passage corresponding to the bias magnet 13 to face it, as shown in FIGS. 24 and 25. If the disk 4 has data storage portions on both the sides of the disk, one of the upper and lower sides of the cassette body 17 has the opening 18a as such a passage for the optical head 5 or the bias magnet 13, and the other opening 18b as such a center hole for the hub 16, and the other of the sides has the yet other opening 18a as such a passage for the magnet or the head, and the yet other opening 18b as such a center hole for the hub.
Since the conventional apparatus has the only one optical head 5 and the only one bias magnet 13, each of the upper and lower sides of the body 17 of the cassette 15 needs to have only one opening 18a as a passage for the head or the magnet. For that reason, the space in which the shutter 19 for preventing dust or the like from entering to the data storage surface of the disk 4 through the openings 18a and 18b is provided on the cassette body 17 can be secured thereon.
A conventional magneto-optical disk drive and read/write apparatus includes a bias magnet device 54 which is located near one side 52b of a magneto-optical disk 52 and opposed to an optical head 53 which faces the data storage side 52a of the disk, as shown in FIG. 26. To erase existing data and then record new data in the data storage surface 52a of the disk 52, a semiconductor laser beam of high intensity is projected to a prescribed position on the data storage surface through the optical head 53 to heat the storage film of the beam-irradiated portion of the disk above the Curie temperature thereof of make the direction of the magnetization of he film coincide with that of the magnetic field of the bias magnet device 54, thus erasing the existing data. By the time the disk 52 is thereafter reacted by another round to have the same positional relationship with the head 53 and the magnet device 54 as set at the time of the erasure, a direction is selected for the magnetic field of the bias magnet device 54 depending on the direction of magnetization for the new data. The laser beam is then projected again to the position on the storage surface 52a of the disk 52 through the head 53 to heat the storage film of the beam-irradiated portion of the disk, thus recording the new data in the portion through the magnetization thereof depending on the direction of the magnetic field of the magnet device 54.
To reproduce recorded data from the disk 52, the laser beam is lowered in intensity and projected to the recorded position of the data on the disk through the optical head 53. At that time, the direction of the rotation of the plane of polarization of disk-reflected light changes depending on the direction of the magnetization of the data storage film of the beam-irradiated portion of the disk 52. The changed direction is detected to read or reproduce the data.
If the apparatus is a conventional one for a magneto-optical disk of 5.25 inches or 130 mm in diameter, the bias magnet device 54 includes a movable part 59 having a permanent magnet 55 and shafts 56 supporting the magnet at the both ends thereof, plain bearings 60 supporting the movable part 59 at the shafts 56 rotatably, and a coil 61 for turning the movable part over. To record data in the disk 52, the direction of an electrical current for the coil 61 is altered to turn the movable part 59 over to select a direction for the magnet field of the permanent magnet 55 depending on the data.
The permanent magnet 55 is disposed so that the axis thereof extends along the radial direction of the disk 52. Since the magnet 55 is not moved along the radial direction of the disk, the axial dimension of the magnet needs to be not less than the radial dimension of the data storage surface 52a of the disk. The magnet 55 is usually made of a rare-earth element to generate a magnetic field strong enough to erase and record data from and in the storage surface 52a of the disk 52.
FIG. 27 shows a conventional device for positioning the optical head of an optical disk drive and read/write apparatus. The movable portion of an optical head 75 is mounted on a carriage 77 so as to be moved by a linear motor 78 along the radial direction of an optical disk 74 to position the head at the aimed track of the disk. At that time, the number of lead grooves 74a provided in the disk 74 in advance as shown in FIG. 28 is counted to seek the aimed track to position the head 75 thereat.
FIG. 29 shows magneto-optical disk and read/write apparatus which is a conventional drive and read/write apparatus for an optical disk. In the apparatus, a turntable 82 is supported with ball bearings 83 by a housing 81 so that the turntable can be rotated by a motor 84. The magneto-optical disk 85 is clamped to the turntable 82 so as to be handled by the apparatus. An optical head 86 and a bias magnet 87 are opposed to each other across the disk 85. The head 86 is supported by the housing 81 and a linear motor 88 which is for moving the head. The head 86 is moved along the radial direction of the disk 85 by the linear motor 88 to read or write data in a prescribed position from or in the disk or to erase, record or reproduce a signal from or in the disk.
When the disk 85 which is a data storage medium is in use, it is housed in a cassette 90 shown in FIG. 30 and 31. The cassette 90 includes a body 91 in which the disk 85 is rotatably housed. The body 91 has opening which are passages 92a corresponding to the range of the movement of the optical head 86, and a center hole 92b corresponding to a hub 93 for clamping the disk 85 to the turntable 82. The cassette 90 also includes a shutter 94 for preventing dust or the like from entering to the surface of the disk 85 through the openings. The disk 85 is a one-side data storage disk having a data storage portion on only one side of the disk, or a both-side data storage disk having data storage portions on both the sides of the disk. If data stored in one side of the both-side data storage disk is to be read or reproduced therefrom by the conventional drive and read/write apparatus, the disk is clamped to the turntable 82 so that the side faces the optical head 86. When data stored in the other side of the both-side data storage disk is to be read or reproduced therefrom by the apparatus, the disk is clamped to the turntable 82 so that the side faces the optical head 86.
FIG. 32 shows a conventional divided-type optical head 01 for an optical disk drive and read/write apparatus. The head 01 is dividedly made of a moveable optical system 02 of relatively small weight, and a fixed optical system 03 of relatively large weight. The movable optical system 02 has a carriage 08 including an upward diverting mirror 05 for diverting a horizontally-incident laser beam 04 upward, and an objective lens 07 for forming a small spot of the beam on the surface of an optical disk 06. The carriage 08 is moved along the radial direction of the disk 06 by a linear motor not show in FIG. 32, to position the small spot of the beam 04 on the aimed track of the disk.
However, the conventional drive and read/write apparatus for the magneto-optical disk shown in FIGS. 23-25 has a problem that the apparatus is lower in access speed and data transfer speed than a magnetic disk drive and read/write apparatus so as to make it impossible to fully utilize the advantage of the former apparatus that the magneto-optical disk is high in storage capacity and can be replaced. In other words, since the erasure, recording and reproduction of data are performed through the single optical head of the former apparatus and the disk needs to be rotated by one round for each of the erasure, recording and reproduction, the recording of new data in the disk takes time during which the disk is rotated by two or three rounds. Even if the rotation speed of the disk is heightened to cope with the problem, the heightening is limited by the output power of the semiconductor laser module and the sensitivity of the disk so that it is difficult to shorten the time of data recording in the disk. It is also difficult to heighten the rotation speed of the disk to shorten the time of data reading or reproduction from the disk. As a result, the problem remains unsolved.
Accordingly, it is an object of a first aspect of the present invention to provide an optical disk drive and read/write apparatus in which the time which is takes for the apparatus to perform the erasure, recording and reproduction of data from and in an optical disk is shortened to heighten the access speed and data transfer speed.
To heighten the data storage capacity of the magneto-optical disk 52 as shown in FIG. 26, the diameter thereof is increased to enlarge the data storage surface 52a of the disk. If the diameter is increased, the axial dimension of the permanent magnet 55 of the bias magnet device 54 needs to be augmented. However, if the magnet 55 is made of the rare-earth element, the magnet is not high enough in mechanical tenacity and is therefore difficult to process and easy to break. In that case, the magnet 55 requires much carefulness in handing, and is difficult to be made large in length. This is a problem. For that reason, if the magnet 55 is to be lengthen, it cannot be made of the rare-earth element generate strong magnetic field to allow the use of a magneto-optical disk of low magnetizability.
Accordingly, it is an object of a second aspect of the present invention to provide a large-sized bias magnet device in which a bias magnet made of a rare-earth element to have strong magnetism can be included for even a magneto-optical disk whose diameter is not less than 12 inches (300 mm).
In order to detect track information from the lead grooves 74a of the optical disk 74 through the optical head 75 to position it at the aimed track of the disk, the conventional device shown in FIGS. 27 and 28 needs to seek the track through tracking servo control while vertically and slightly moving the objective lens of the head through the focusing servo control of the objective lens actuator (which is a two-axis actuator) of the head to always focus a laser beam on the surface of the disk. Because of the responding properties of mechanisms for the tracking and focusing control, there is a limit on the increase in the speed of the seeking of the aimed track. This is a problem.
Since the seeking of the aimed track is likely to be affected by the eccentricity between the axis of the disk 74 and that of a rotary motor for the disk and the warp of the disk, the number of the lead grooves 74a of the disk tends to be miscounted at the time of rapid seeking of the track so that it takes more time to position the optical head 75 at the track, and that in an extreme case, the tracking servo control fails to be properly done for the positioning. This is also a problem.
The present invention was made in order to solve the above-mentioned problems. Accordingly, it is an object of a third aspect of the present invention to provide a device for rapidly and accurately positioning the optical head of an optical disk drive and read/write apparatus at the aimed track of an optical disk.
The conventional drive and read/write apparatus for the optical disk shown in FIGS. 29-31 is lower in access speed and data transfer speed than a magnetic disk drive and read/write apparatus. This is a problem. For that reason, the feature of the optical disk that it is high in storage capacity and can be replaced with another one cannot be fully utilized.
As for the conventional apparatus, each of the erasure, recording and reproduction of data is performed through the only one optical head, and requires that the optical disk is rotated by one round. To record new data in the disk, a light beam is emitted from a semiconductor laser module and concentrated to the position of the recording in the disk through the optical head 86 to heat the beam-irradiated portion of the disk by the spot of the beam thereon to magnetize the portion in the direction of the magnetic field of the bias magnet 87 to erase existing data from the portion first. By the time the optical disk 85 is thereafter rotated by another round to have the same positional relationship with the optical head 86, a direction is selected for the magnetic field of the bias magnet 87 so as be coincident with the direction of magnetization of the portion of the disk for new data. The portion is then heated again by the spot of the beam thereon so as to be magnetized in the selected direction of the magnetic field of the magnet 87 to record the new data in the portion. The disk 85 is thereafter rotated by yet another round to check whether the new data have been precisely recorded in the disk, if necessary. Therefore, the recording of such new data in the disk 85 requires the two or three rounds of rotation of the disk 85, and therefore takes much time. This is also a problem.
To record data in both the sides if the both-side data storage disk by the apparatus, the data is recorded in one of the sides first, and thereafter recorded in the other of them. This is a problem of inconvenience. Even if the rotated speed of the disk is increased to cope with problem, the speed is limited by the output power of the semiconductor laser module an the sensitivity of the disk to make it difficult to shorten the time of the recording.
Since the only one optical head 86 is provided to face one side of the disk 85, data stored in both the sides thereof cannot simultaneously be read or reproduced therefrom. Particularly when it is not known the side which is the data is stored in, the disk often needs to be turned over to search for the stored position of the data. This is a problem of long time consumption.
Accordingly, it is an object of forth and fifth aspects of the prevent invention to provide an optical disk drive and read/write apparatus shortened in the time of erasure, recording and reproduction of data from and in an optical disk, short in access time, high in data transfer speed, and capable of erasing, recording and reproducing data from and in the disk on both the sides thereof simultaneously.
Since there is a slight clearance between the bearing and guide of the linear motor, the carriage 08 of the conventional optical head 01 as shown in FIG. 32 performs a pitching motion about an axis X, a rolling motion about an axis Y, and a yawing motion about an axis Z as the movable optical system 02 is moved along the radial direction of the optical disk 06, in the direction of the axis Y perpendicular to the other axes X and Z perpendicular to each other. For that reason, the optical axis for the laser beam 04 to the upward diverting mirror 05 of the movable optical system 02 deviates, and the incident angle of the beam to the mirror fluctuates. As a result, the efficiency of concentration of the laser beam 04 to the surface of the optical disk 06 is deteriorated. This is a problem.
The problem is described in detail with reference to FIG. 32 from now on. The upward diverting mirror 05 and the objective lens 07 are put in a prescribed positional relationship with each other at the time of assembly of the carriage 08. If the carriage 08 is tilted by a pitching angle 8 due to the pitching motion of the movable optical system 02 as it is moved by the linear motor, the incident angle of the laser beam 04 from the fixed optical system 03 to the mirror 05 deviates by the pitching angle from a proper value so that incident angle of the beam to the objective lens 07 changes by the tilting angle .theta. thereof from the vertical plane extending through the lens. As a result, the incident angle of the beam 04 to the surface of the disk 06 changes by the sum 20 of the pitching angle 0 and the tilting angle .theta.. Therefore, the efficiency of concentration of the beam 04 to the surface of the disk 06 is deteriorated from that in the case of the normal perpendicular incidence of the beam to the surface of the disk.
If the diameter of the optical disk 06 is increased to heighten the capacity thereof, the length of the movement of the carriage 08 along the radial direction of the disk is segmented to make it more difficult to reduce the pitching, rolling and yawing notions of the movable optical system 02.
Accordingly, it is an object of a sixth aspect of the present invention to provide an optical head which operates so that even if the carriage of the movable optical system thereof fluctuates in posture or performs a pitching motion during the movement of the system, a laser beam is irradiated upon the surface of an optical disk through the head perpendicularly to the surface of the disk does not move up and down but rotates on a prescribed plane.